Precision or site specific farming describes a particular farming practice where inputs are varied according to need. In order to establish need, the farmer obtains or creates maps showing how different parameters vary in value across any particular field.
One type of map commonly used is the yield map. The data for yield maps is collected by the harvesting machine using yield meters. For example, WO96/38714 describes a yield meter which measures the flow of grain using electromagnetic waves. It is also known to measure yield by weighing each tank of grain harvested.
In order to provide data suitable for the production of a yield map, the harvesting machine on which the yield meter is mounted must be equipped with positioning equipment, thereby enabling yield to be associated with location. Data from the yield meter is then recorded at data recording points, and at each data recording point the position of the harvesting machine is also recorded. A yield map is then established by processing the raw data using yield mapping software.
Using the yield map, the farmer can then plan the inputs for the following year's crop. For example, where yield is low he may add more fertilizer, or upon investigation he may find that the low yield was associated with compaction, and he may elect to cultivate that particular are of the field to a greater depth that the other areas.
The accuracy of yield maps depends on the accuracy of the data collected. Clearly, the more accurate the yield map, the more valuable it is to the farmer as a management tool. There are numerous ways of increasing the accuracy of yield maps. The present invention proposes a convenient and cost effective method for establishing accurate yield maps.
It is known to apply a correction factor to a yield data set. However, the known method relies upon comparing the total yield for a field as measured on the harvesting machine with the total yield for the field as measured by a second weighing system, comparing the two and using the difference as the correction factor, i.e., the yield as weighed by the second weighing system is deemed to be the accurate measurement. The correction factor is then applied to each datum in the data set. This method assumes a constant error in the yield meter mounted on the harvesting machine. However, the error may well not be constant. For example, it has been noticed that when harvesting oily crops, the error in the yield meter on the harvesting machine increases throughout harvesting due to the build up of sticky crop residues in the body of the yield meter.
As well as measuring yield on a harvesting machine, it is also known to measure moisture content of the crop being harvested, for example on a combine harvester. U.S. Pat. No. 5,561,250 discloses a combined yield and moisture meter for use on a combine harvester.
However, the type of moisture meters used on combine harvesters are inaccurate due to the way moisture is measured. They rely on the capacitance effect, which effectively measures the moisture content on the surface of the grain. The surface moisture content does not necessarily equate to the moisture content in the grain kernel.
It is not common practice to map grain moisture content, even though a moisture meter may be present on the combine. Where a moisture meter is present on the combine harvester it is not known to adjust the yield recorded according to moisture content.
However, it is known that moisture content can vary within a field, and with the time of day. For example, in Brazil the moisture content of grain can fall from 14% to 8% and rise again to 14%. Without correcting for moisture content the yield map would show a lower yield where the moisture content fell, and an increased yield where the moisture content rose.
It is an object of the invention to provide a method, which allows inaccuracies in yield maps to be corrected.
A yield meter usually measures a parameter which is indicative of yield, rather than weighing the crop itself. In this specification the term “measuring yield using a yield meter” will be understood to encompass the yield meter either measuring a parameter indicative of yield, or weighing the crop itself.